/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.runtime.rest.handler.job.checkpoints;

import org.apache.flink.runtime.checkpoint.AbstractCheckpointStats;

import org.apache.flink.shaded.guava18.com.google.common.cache.Cache;
import org.apache.flink.shaded.guava18.com.google.common.cache.CacheBuilder;

import javax.annotation.Nullable;

/**
 * A size-based cache of accessed checkpoints for completed and failed checkpoints.
 *
 * <p>Having this cache in place for accessed stats improves the user experience quite a bit as
 * accessed checkpoint stats stay available and don't expire. For example if you manage to click on
 * the last checkpoint in the history, it is not available via the stats as soon as another
 * checkpoint is triggered. With the cache in place, the checkpoint will still be available for
 * investigation.
 */
public class CheckpointStatsCache {

    @Nullable private final Cache<Long, AbstractCheckpointStats> cache;

    public CheckpointStatsCache(int maxNumEntries) {
        if (maxNumEntries > 0) {
            this.cache =
                    CacheBuilder.<Long, AbstractCheckpointStats>newBuilder()
                            .maximumSize(maxNumEntries)
                            .build();
        } else {
            this.cache = null;
        }
    }

    /**
     * Try to add the checkpoint to the cache.
     *
     * @param checkpoint Checkpoint to be added.
     */
    public void tryAdd(AbstractCheckpointStats checkpoint) {
        // Don't add in progress checkpoints as they will be replaced by their
        // completed/failed version eventually.
        if (cache != null && checkpoint != null && !checkpoint.getStatus().isInProgress()) {
            cache.put(checkpoint.getCheckpointId(), checkpoint);
        }
    }

    /**
     * Try to look up a checkpoint by it's ID in the cache.
     *
     * @param checkpointId ID of the checkpoint to look up.
     * @return The checkpoint or <code>null</code> if checkpoint not found.
     */
    public AbstractCheckpointStats tryGet(long checkpointId) {
        if (cache != null) {
            return cache.getIfPresent(checkpointId);
        } else {
            return null;
        }
    }
}
